1. Field of the Invention
The present invention relates to lightweight gas masks for use in protecting personnel from exposure to chemical and biological agents. More specifically, it relates to protective head and shoulder covers with chemical air filters that protect lungs, face, head and upper body from contact with toxic chemical and biological agents.
2. Description of the Prior Art
Protective masks, often called gas masks, have been widely used by the military, industry and emergency civil organizations to protect civilian and military personnel from exposure to a variety of toxic airborne agents. Since the advent of gas warfare in World War I, the military has developed a variety of gas masks. Some of the most critical problems confronting developers of such masks have been associated with the following mask features: weight, size, stowage, fit, comfort, optical compatibility and breathing resistance. Although such prior art devices have generally served the purpose, they have not proved entirely satisfactory under all conditions of service.
More specifically, the Army's most current protective masks include the M40, intended for use by the infantry, and the M42, intended for use by tankers. The M40 face piece, protective hood, filter canister and carrier weigh approximately 3.8 pounds and accumulate a packaged space of approximately nine inches by eleven inches by four and one-half inches. The M40 mask has a flexible face piece so that it may be folded for storage in the carrier along with the hood, a filter, a winterization kit, etc. The loaded carrier is carried by the soldier with a sling shoulder strap and a waist strap. The face piece, made from silicone, has a peripheral seal designed to provide a comfortable seal on the user's face. Although the eye relief of the M40 is closer than that of a previous Army mask (M17), it still has problems in coupling with certain optical sighting devices. Also, to accommodate left and right handed firing, the M40 must exchange its filter canister from one side to the other side of its face piece. Although a generally acceptable breathing resistance is achieved in the M40, many users still complain of its high breathing resistance especially at high work rates.
The M40 series of masks was primarily designed for the military, however similarly constructed masks as the M40 have also found important civilian uses. For instance, protective masks are routinely used by agricultural personnel during periods of herbicide and pesticide spraying. Other civilian users of protective masks include workers in the chemical industry, biological researchers and fire fighters.
The primary thrust in current U.S. Army plans for the future battlefield is to lighten the soldier's load. However, some bulky protective gear, such as the current gas masks, must be carried by the soldier whether there is an immediate need for it or not. The size and weight of the M40 mask precludes its use in many special "light forces" applications. The M40, even though it can be rolled up in the carrier, occupies too much space for even normal combat operations, in the opinion of many combat soldiers.
Further, many users of gas masks often find them uncomfortable to wear. The suspension system of the M40 series includes thick strapping and metal buckles which cause hot spots on the wearer's head. Also, the M40 hood is not conformable and is bulky which, under many circumstances, causes movement to be awkward. The combined weight of the M40 mask, hood and canister can cause neck strain when it is worn for an extended period. The relatively heavy C2 filter canister bounces when the user moves quickly, often causing the mask to jerk the wearer's head.
Optical compatibility is another problem users often encounter with conventional gas masks. The eye relief of the M40 mask is about 45 millimeters. The recommended eye relief for proper use of most optical equipment is typically 25 millimeters. As such, many sighting devices within the Army's inventory either cannot be used with the M40 mask or the user's field of view is significantly reduced. Also, when the filter canister is mounted on the face piece, it can often pose optical compatibility problems with many weapon systems, fire fighting equipment, rescue apparatus and the like.
Still further, users of protective masks often experience physiological problems associated with high inhalation and exhalation resistances caused by current flapper-valve and canister-filter combinations. For example, the C2 canister, used in the M40 series of masks, produces 45 millimeters of H2O resistance when measured at a flow rate of 85 liters per minute. Many users find that resistance to by unduly high, particularly in stressful situations.
Consequently, those concerned with the development of protective masks have long recognized the need for substantial improvements in mask design. The present invention fulfills this need.